The present invention relates to an apparatus and associated method for decontaminating contaminated matter such as objects and substances and, more particularly, to a pressurizable ultrasonic cleaner having an enhanced transient cavitation effect due to the addition of a volatile substance to a cleaning solution and pressurization thereof during the ultrasonic decontamination process.
Infection control is essential to medical and dental practices. Indeed, the Center for Disease Control, medical associations, dental associations and various states are passing laws and guidelines to increase the infection control measures that must be taken by dentists and physicians. In particular, concerns over patient to patient or staff to patient transfer of various diseases and viruses such as hepatitis B virus, HIV and other diseases have been on the rise. It is believed that most disease transfer is primarily due to the continual reuse of instruments. Therefore, efforts to combat disease transfer have generally focused on sterilizing instruments through the use of one or more of six sterilants: steam, chemical vapor, dry heat, chlorine dioxide, ethyl oxide, glutaraldehyde-containing liquid, and formaldehyde. McErlene et al., xe2x80x9cAssessment of the Effectiveness of Dental Sterilizers Using Biological Monitorsxe2x80x9d, J. Can. Dent. Assoc.58(6):481-83 (1992); B. Nystrom, xe2x80x9cNew Technology for Sterilization and Disinfectionxe2x80x9d, Amer. Jrl. of Med. 91(3B):2645-2665(1991). However, the above-listed sterilants, alone and in combination, often fail to adequately, and space and cost effectively, provide a safe means for sterilization. McErlene et al., xe2x80x9cAssessment of the Effectiveness of Dental Sterilizers Using Biological Monitorsxe2x80x9d, J. Can. Dent. Assoc. 58(6):481-83 (1992);B. Nystrom, xe2x80x9cNew Technology for Sterilization and Disinfectionxe2x80x9d, Amer. Jrl. of Med 91(3B):2645-65 (1991); and N. Skaug, xe2x80x9cProper Monitoring of Sterilization Procedures Used in Oral Surgeryxe2x80x9d, Int. J. Oral Surg. 12:153-58 (1983).
The high percentage of sterilization ineffectiveness was highlighted in one alarming study that showed that 33% of the autoclaves used in general dental practice did not inactivate microbes. Simonsen et al., xe2x80x9cAn Evaluation of Sterilization by Autoclave in Dental Officesxe2x80x9d, J. Dent. Res. 58(A):Abstract No. 1236 (1979). And, in an even more alarming study of instrument sterilization procedures in oral surgery clinics, 23% of steam autoclaves; 50% of dry-heat oven sterilizers; and 100% of gas autoclaves did not kill biological spores. N. Skaug, xe2x80x9cProper Monitoring of Sterilization Procedures Used in Oral Surgeryxe2x80x9d, Int. J. Oral Surg. 12:153-58 (1983).
Moreover, several other recent studies have shown that autoclave and heat sterilization routinely do not sterilize instruments. See Palenik, xe2x80x9cEffects of Steam Sterilization on the Contents of Sharps Containersxe2x80x9d, Am. J. Infect. Control, 21(1):28-33 (February 1993); Palenik et al., xe2x80x9cEffectiveness of Steam Sterilization on the Contents of Sharps Containersxe2x80x9d, Clin. Prev. Dent., 14(1:28-34 (January-February 1992); B. Nystrom, xe2x80x9cNew Technology for Sterilization and Disinfectionxe2x80x9d, Am. J. Med., 91(3B):264S-266S (Sep. 16, 1991); and Palenik et al., xe2x80x9cEffectiveness of Steam Autoclaving on Bacterial Endospores Placed Within Five Types of Sharp Containers Was Testedxe2x80x9d, Am. J. Dent 3(6)239-44 (December 1990) of dental and medical instruments are not adequately decontaminated by various combinations of presoaking agents, dishwashers, ultrasonic cleaners, detergents and water. E. Sanchez and G. MacDonald, xe2x80x9cDecontaminating Dental Instruments: Testing the Effectiveness of Selected Methodxe2x80x9d, JADA 126:359-68 (March, 1995). In fact, the effective sterilization of many instruments has been so unreliable that instruments are being redesigned to facilitate effective cleaning and disinfection. Spach et al., xe2x80x9cTransmission of Infection By Gastrointestinal Endoscopy and Bronchoscopyxe2x80x9d, Annals of Internal Medicine 118:117-28 (1993).
In addition to inadequate sterilization equipment, problems with sterilization methods also occur because of human error. Moreover, the expense and cost of safe effective sterilization techniques may force or otherwise influence the use of less effective sterilization techniques and equipment.
When properly applied, the ultrasonic cleaning process has been shown to be beneficial for deburring and debriding various instruments and tools. Ultrasonic energy consists of vibrations or sound waves above frequencies normally heard by the human ear. Typically, an ultrasonic generator is used to produce high frequency alternating electrical currents, which are transformed into mechanical ultrasonic vibrations by a transducer. The vibrations are then transmitted into liquids consisting of either water-based or solvent-type solutions which, in turn, contact the surfaces of the object to be cleaned. Thus, the ultrasonic energy engages the object via the liquid medium to remove contaminants therefrom and/or to destroy microbial matter.
Ultrasonic cleaning increases decontamination effectiveness to a level that is difficult to achieve by other means. Over the past several years, practical ultrasonic cleaning applications have grown rapidly. For example, it is known in the art that ultrasonic transient cavitation used in conjunction with germicidal solutions will kill microbes more quickly than will a similar solution in the absence of ultrasonic transient cavitation. R. M. G. Boucher, Ph.D., xe2x80x9cUltrasonicsxe2x80x94A Tool to Improve Biocidal Efficacy of Sterilants or Disinfectants in Hospital and Dental Practicexe2x80x9d, Can. Jrl. of Pharmacology, 17(1):1-12 (1979). However, there are currently no methods employing ultrasonic vibration as the only means of decontaminating contaminated matter such as medical or dental instruments. In current processes, instruments or objects being decontaminated are typically moved from an ultrasonic cleaning device into an autoclave for further sterilization. xe2x80x9cDecontaminationxe2x80x9d is used herein to encompass the broadest meaning of the term and includes, for example, deburring, debriding, sterilizing, or otherwise effecting cell disruption of contaminated objects, substances, or fluids.
A need therefore exists for an apparatus and method for decontaminating contaminated matter such as dental and medical instruments that is quiet, convenient, easy to use, inexpensive, and preferably heat-independent. It would further be desirable for the apparatus and method to operate at or near room temperature such that, for example, the xe2x80x9ccoldxe2x80x9d sterilized instruments can be rinsed, dried off and used immediately after sterilization without having to first cool down the instruments. A need further exists for an apparatus and method of improving the efficiency of ultrasonic cleaning for decontaminating contaminated matter such as medical and dental instruments such that further sterilization processes are not required for acceptable decontamination.
The above and other needs are met by the present invention which, in one embodiment, provides an apparatus for decontaminating contaminated matter comprising a pressurizable container for containing the contaminated matter, a pressure source for pressurizing the pressurizable container to a predetermined pressure, a vibration source operably connected to the pressurizable container, and a cleaning solution contained within the pressurizable container and submerging the contaminated matter. Preferably, the cleaning solution comprises a base solution and a predetermined amount of a volatile substance that is more volatile than the base solution. The cleaning solution is then pressurized by the pressure source and vibrated by the vibration source to produce ultrasonic transient cavitation therein for decontaminating the contaminated matter. The contaminated matter may comprise, for instance, medical or dental instruments, or may comprise other substances such as, for example, a fluid. Further, the pressurizable container is capable of being pressurized to greater than about 1 atmosphere, while the pressure source is capable of pressurizing the cleaning solution therein to a pressure of greater than about 1 atmosphere. Generally, the pressure to which that cleaning solution is subjected is a function of, for instance, the composition of the cleaning solution and the concentration of the added volatile substance. In some advantageous embodiments, the cleaning solution is an aqueous cleaning solution pressurized to about 2.4 atmospheres. In addition, the vibration source is capable of vibrating the cleaning solution to produce ultrasonic transient cavitation therein between the cleaning solution and the contaminated matter. Preferably, the cleaning solution comprises a base solution and a predetermined amount of a substance more volatile than the base solution, and the cleaning solution is capable of decontaminating the contaminated matter without leaving a harmful residue.
A further advantageous aspect of the present invention comprises a method for decontaminating contaminated matter, including the steps of containing a cleaning solution having a predetermined amount of a volatile substance within a pressurizable container, submerging the contaminated matter in the cleaning solution, pressurizing the cleaning solution to a predetermined pressure, and vibrating the cleaning solution to produce ultrasonic transient cavitation therein. Preferably, the pressurized cleaning solution and the presence of the volatile substance therein enhances the effect of ultrasonic transient cavitation to thereby improve decontamination of the contaminated matter. Preferably, the cleaning solution comprises a base solution and a predetermined amount of a substance more volatile than the base solution, and the cleaning solution is capable of decontaminating the contaminated matter without leaving a harmful residue. The method further comprises pressurizing the cleaning solution to a pressure of greater than about 1 atmosphere while vibrating the cleaning solution to produce ultrasonic transient cavitation therein between the cleaning solution and the contaminated matter.
Thus, embodiments of the apparatus and the method for decontaminating contaminated matter according to the present invention advantageously provide enhanced ultrasonic transient cavitation due to the addition of a volatile substance to the cleaning solution that, when pressurized and vibrated, is capable of decontaminating contaminated matter without leaving a harmful residue in a cost-effective and quiet manner while not overheating the matter being decontaminated. The ultrasonic cleaning device according to the present invention is generally convenient, easy to use, inexpensive, and operates at or near room temperature in a xe2x80x9ccoldxe2x80x9d sterilization process which allows the matter to be utilized immediately following the sterilization process. With the ultrasonic cleaning device according to the present invention having a pressurized cleaning solution containing a volatile substance, an enhanced and more efficient ultrasonic cleaning process is provided for decontaminating contaminated matter, such as medical and dental instruments.